relation to mankind
contain genetic material in the form of DNA or RNA and interact with hosts and
vectors carriers under the canopy of environment. These interactions cause
several lethal diseases in major crops i.e. rice, wheat, maize, sugarcane and
sorghum besides horticultural, medicinal and ornamental crops.
devastating viruses of plants are Rice Tungro Virus, Wheat Dwarf Virus, Maize
Streak Virus, Coconut Cadang Cadang and Bean yellow mosaic virus of Gladiolus.
Similarly human and animal viral diseases like Hepatitis, Dengue, Influenza,
AIDS, Herpes, Foot and Mouth disease etc. adversely affect human and animal
Environmental factors influence the incidence of diseases caused by these
viruses in several ways:
may favour the multiple of a given vector of the virus leading to a rise in its
population. This automatically leads to wider spread of the virus which leads
to higher incidence of the disease.
may adversely affect the population of an antagonist of a vector which once
again leads to a rise in the vector population.
environment adversely affects the population of the vector itself then the
disease is unable to spread widely and its incidence drops.
alternate host of the virus may have a population explosion which leads to a
great rise in the availability of viral inoculum for spread to human or crop
agriculture, indiscriminate use of pesticides sometimes leads to the great
reduction in the population of an antagonist of a vector. The vector
population, being free from any antagonism now rises rapidly and the incidence
of the disease transmitted by this vector rises.
outbreak of plague in
confirms the importance of environmental factors in the incidence of viral
on to understand and manage these diseases to eliminate or minimize their ill
effects on the society. Recent developments in molecular biology have provided
tools for quick and reliable diagnosis of various viral pathogens both in
plants and animals. This means that most diseases can now be detected before
they assume alarming proportions. It also helps us to find out the various
ecological niches in which the virus survives.
viruses (e.g. Nuclear Polyhedrosis Virus) are responsible for keeping insect
populations under check. Some fungi also kill insects.
But if our
pesticides eliminate these fungi then insect population will rise and so will
the incidence of any disease transmitted by them.
biology is helping us to design highly effective vaccines based on detailed
knowledge of the surface proteins of the virus and better vaccine delivery
We have to
manage our environment such that the viruses, their vectors and we (or our
crops) can all coexist without any significant disadvantage or advantage to
anyone of them. Only balance can bring health.
Dr. B.P Singh, former head of the Plant Pathology and
Protection Division, NBRI is currently an Emeritus Scientist at the National
Botanical Research Institute, Lucknow (India),